Just wanted to add that looks somewhat suspiciously like calcium deficiency. I use RO water for my plants and noticed new growths blackening and with added fert things have been much better. CA deficiency can look look like bacterial rot- black dieback of leaves, but usually affects new growths. It takes time to improve things but seems like your culture otherwise is sufficient. RO, Distilled, Rain water can be too pure, and can almost be acidic in the way it affects things if you water with that as base. It can wipe out any nutrients, so it may be worth thinking about this as well.

I grow plants inside and out here in california, and most of the neos have stayed inside and grow fine. In fact after much research before building my neo collection recently I found many growers do better with them inside under lights with mostly steady parameters anyway. The ones outside can handle cold and dry but they tend to look pretty ratty by spring, although they do flower better. I enjoy the foliage more so I'd rather see a balanced growing plant. I still get blooms, however just not the show you could get with more cold. My neos are watered a bit less in winter but still pretty much get daily to every other day watering even in moss mounds. They really can handle a fair amount of watering as long as they get to dry out some. Of course, I have dryer conditions here but on other hand seems like folks with houses in colder climates have humidity levels tank in winter more than here. With temps as warm as you have them I wonder if maybe more water would help the growths come in. Other than rot, too little water can damage older roots. but they seem to always reroot come spring.

Also wanted to note, neo hybrids tend to need slightly different culture. Noticing the very red leaves on your plants in the pics- while pretty generally means a fair amount of stress, if not just high light. lower light levels can help with the neo side to them. Also vanda species in them tend to need more fert than just the straight neos which to me prefer purer water over long term.

I have dealt with suspected calcium deficiency with catts. I use K-Lite fertilizer which has calcium, and a combination of bottled spring water and grocery store RO water (which has TDS around 200 so I think it still has minerals, it claims to have no fluoride and no chlorine). In the summer months, I'll use tap or hose water, we have very hard water.

In looking back, I think my mistake with the neo that died was that I soaked it too deeply and got the base of the plant too wet, for too long. I was thinking along the lines of vandas needing regular soakings (outside of southern climates at least) and went overboard.

I did repot the ones that were in moss, and they were all in good shape. Watering once a week for now. I did a Cleary's flush on all of them. Their light exposure is southern window and T5HO. It could be a fungus, but I'm not spraying them with anything at this point. The Lou Sneary has gotten very spotted with black, so I am watching it with emotional detachment to see what happens next. On the other hand, I have some really healthy looking specimens and will hopefully keep them that way!